From MangaHelpers:

Luca's friend Will, who is from a lower-class segment of society, has gone missing. Luca's only clue to find his friend is his fondness for a certain club in the entertainment district, where a woman named Yue performs. Will had always said they should go there together sometime.
When Luca goes down alone to try to speak to Yue, though, he ends up being beaten badly. Luckily, Yue herself finds him, and takes him to her friend Takaomi to be patched up. It soon becomes clear that Will has fallen victim to a chimera sickness that is becoming common in the lower classes. Luca is determined to find his friend, and to save him.